EP 0 295 655 B1 describes a roll of this type in which the internal heating system extends over the same width as the external heating system and is continuously in the active state during normal operation so as to minimize the temperature difference between the outer and the inner surface of the roll shell in order to prevent excessive stress from being generated in the material of the roll. The document recognizes that unacceptably high stress is created in the roll if one or the other of the two heating systems becomes inactive.
DE-OS 38 14 794 describes a technique whereby the shell of a load-deflection compensating roller, supported by a rotationally fixed arbor, is internally heated by a liquid heat carrier while an inductive external heating device is provided at both ends. This approach permits the utilization of a larger effective width of the roll.
Similar solutions in which the ends of the roll shell are heated by means of a liquid heat carrier are described in DE 41 07 440 C1 and DE 93 01 416 U1.
DE 30 14 891 C2 describes a calender roll which is heated only from within by means of a liquid heat carrier. The end sections of the roll are supplied with a heat-carrying liquid by way of special ducts, separate from the roll main section between its two ends. This results in a very complicated internal structure of the roll. The desired effect is always to obtain a thermally even, cylindrical surface over the full length of the roll when it is heated. The problem is therefore related to the functional operation of the roll rather than the heating process.